5 Exoplanets May Orbit Nearby Sun-Like Star Tau Ceti

A nearby sun-like star called Tau Ceti may contain a system of five planets, including one that orbits at the right distance to have life.

Tau Ceti has roughly three-quarters the mass of our own sun and is among one of the 20 closest stars, located 12 light-years away in the constellation Cetus. Because it is easily visible to the naked eye and can be seen from both the Northern and Southern Hemisphere, it is well-studied. Scientists know that it has a dusty debris disk at least 10 times more massive than our solar system’s Kuiper Belt and have observed it for long enough to rule out it having any planets larger than Jupiter.

The new exoplanets were found by looking for a characteristic wobble in the star’s orbit that indicates a planet is tugging on it gravitationally. A team of astronomers reanalyzed archival data from three different telescopes that previously studied Tau Ceti. Using a branch of mathematics called Bayesian statistics, the team was able to see much finer detail in the wobbly signal than ever before.

The analysis turned up five planets between two and seven times the mass of Earth. One planet, with 4.3 Earth masses, has an orbit of 168 days, placing it at the right distance to potentially contain liquid water. Because the statistical method has not been employed much for planetary searches and pushes the limits of what Earth-based telescopes can see, the Tau Ceti planets could disappear with further scrutiny.

“However, if this detection is correct and the signals we report are truly of planetary origin, this could yet be one of the best places to look for signatures of life outside the solar system,” wrote astronomer Mikko Tuomi of the University of Hertfordshire in the U.K. in an e-mail to Wired. Tuomi is co-author of the study, which appears today in Astronomy & Astrophysics.

Tau Ceti does not quite have the household recognition of our closest neighboring star, Alpha Centauri, but gets mentioned often in works of fiction such as Star Trek episodes and the novels of Isaac Asimov and Robert Heinlein. The star’s biggest claim to fame might be as the home of villain Dr. Durand Durand in the 1968 movie Barbarella.

Its proximity to Earth has made it the subject of searches for extraterrestrial life. In 1960, astronomer Frank Drake conducted one of the earliest SETI searches, Project Ozma, which looked for radio signals coming from Tau Ceti and another star. The project turned up no alien broadcasts, but having planets around Tau Ceti, as well as the recently discovered Earth-sized world around Alpha Centauri, might make the stars in our vicinity seem more like our own.

“It implies our local neighborhood is full of low-mass rocky planets, and potentially full of other Earths,” said astronomer James Jenkins of the University of Chile, co-author of the research.

But the larger astronomy community is not completely convinced these planets exist. “The analysis is really pushing the envelope in what you can dig out of the data,” said astronomer Greg Laughlin of the University of California, Santa Cruz, who was not involved with the work. Noting that the researchers were careful not to over-interpret their data, Laughlin added that it would probably take at least a few more years of observation to confirm the five-planet system and a much longer time to even begin searching for life on them.

But if the planets were found to be real, it would be a great opportunity, Laughlin said. Our own solar system has no planets with masses between that of Earth and Neptune and none inside the 88-day orbit of Mercury. A nearby system with both these properties would offer an excellent opportunity to study the differences between our solar system and that of many other stellar systems in the universe.